Display the rectangle labelled only along the top (6 cm) and down one side (3 cm). Take three hands-up answers, not open call-outs. Listen for pupils who say the opposite sides must match.

Walk each of the three worked examples aloud, one at a time.

• 6 by 3 — point to each side as you add it, and say the bottom matches the top, the second side matches the first.
• 5 cm square — draw out that all four sides are equal, so it is 4 lots of 5.
• 7 by 2 — fill in the two missing sides first, then add. Add each side once, never twice.

This round is for talking it through together — pupils take turns at the board and the class agrees or corrects out loud.

The widget starts on a 4 cm by 3 cm rectangle. After the first pupil reads its perimeter, drag the rectangle's corner handles to re-set new given sides for the next pupil. Run four or five rectangles in turn (for example 4 by 3, then 5 by 2, then 6 by 4, then 3 by 3, then 8 by 2), each time asking the pupil at the board to fill in the matching opposite sides first, then read off the perimeter. Have the class confirm each opposite pair matches before the total is read. Watch for the common slip of measuring all four sides as if they were different.

This round is the practice bank — pupils take turns at the board, check each answer, and the class confirms before moving on. Show each shape on screen in turn so the class can see the one they are working on, including the L-shape. Keep the board work brisk rather than over-explaining.

For each shape ask which sides are hidden and how the pupil found them, then read the perimeter. The 7 by 4 rectangle is new practice, not a repeat of a modelled example, so give it a moment more. The L-shape stretches the strongest pupils — there are six sides to track and two must be worked out from the others. Callout to keep saying: which sides are hidden, and how do you find them?

Keep this brief. Tie the missing-side idea back to the L-shape in the challenge — finding hidden sides will matter again for more complex shapes.